Practical Applications of the Compressibility Equation, 1998 Finishing and Converting Conference Proceedings

The exponential compressibility equation for modeling the behavior of a pile of paper sheets has two versions. One contains three arbitrary coefficients, K1, K2, and K3. Its use is intended to give an improved fit to experimental data, but when applied practically there are difficulties. The initial contact of the compression machine test dies with the test paper surface changes the values of these coefficients if it is reported incorrectly. If the dies travel some distance before the pressure starts to increase high negative values of K3 result. A practical compromise takes the values of compressive pressure and strain after the pile has come under some load, and works back from this data using only a two-coefficient model to find where the test actually started. In doing so, K3 is no longer needed for goodness of fit, the values for K1 and K2 are unique and no longer affected by K3 or starting point. Data comparisons for quality control purposes are more readily made. Changes in manufacturing conditions, furnish, dryness, and their effects on K1 and K2 may be conveniently studied. K2 CD profiles across reel logs become more meaningful when the numbers are not affected by experimental technique.